Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $108.77   3.373%   $112.4388   $112.44   $112.45   $112.40  
  Purchase #2 $239.46   11.439%   $266.8518   $266.85   $266.85   $266.90  
  Purchase #3 $217.43   6.561%   $231.6956   $231.70   $231.70   $231.70  
  Purchase #4 $23.81   8.319%   $25.7908   $25.79   $25.80   $25.80  
  Purchase #5 $128.85   9.591%   $141.208   $141.21   $141.20   $141.20  
  Purchase #6 $144.91   8.381%   $157.0549   $157.05   $157.05   $157.10  
  Purchase #7 $112.59   11.577%   $125.6245   $125.62   $125.60   $125.60  
  7 purchase totals = $975.82       $1,060.6644   $1,060.66   $1,060.65   $1,060.70